CODEWITHSUNDEEP
pythonarraysnumpy
pgtr3s
pgtr3s

Reputation: 29

expand and populate numpy array

What is the easiest way to expand and populate a python numpy array? Initially the numpy array is:

[[1,3], [1,2], [1,5]]

after expanding, the array should be:

[[1,3,9,27], [1,2,4,8], [1,5,25,125]]

the newly added column is the squared and cubed value of the 2nd column.

Thanks!

Upvotes: 1

Views: 76

Answers (2)

Divakar
Divakar

Reputation: 221524

Slice the second column keeping the dimensions with a[:,[1]], perform the power operations leveraging broadcasting with **[2,3] , because we had kept the dimensions and then stack the output as new columns with np.c_ (one of many ways to stack).

Hence, the implementation -

np.c_[a,a[:,[1]]**[2,3]]

Sample output -

In [902]: np.c_[a,a[:,[1]]**[2,3]]
Out[902]: 
array([[  1,   3,   9,  27],
       [  1,   2,   4,   8],
       [  1,   5,  25, 125]])

Upvotes: 2

PM 2Ring
PM 2Ring

Reputation: 55469

You just need to skip over the 1 in each row, and then use broadcasting to form the desired cartesian product.

import numpy as np

a = np.array([[1,3], [1,2], [1,5]])
b = a[:, 1:] ** np.arange(4)
print(b)

output

[[  1   3   9  27]
 [  1   2   4   8]
 [  1   5  25 125]]

Upvotes: 0

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